In certain regions of the world, during winter months, ice storms can lead to the build-up of ice on the overhead transmission conductor. This ice build-up makes the conductor heavier causing it to sag more and increasing the tension in the line. In the case of a single conductor, the ice buildup can be as large as 50 mm or more in thickness. In the case of multiple conductors (conductor bundle), ice build-up is more common due to the lower operating temperature of the conductors. In this case the ice deposits can “fill” the gap between conductors, and the deposits can cover the entire conductor bundle, leading to a very large diameter, and very heavy, ice deposit. In extreme cases, the ice load can cause line breakage and/or tower failure. The North American storms of 1998, where a large number of towers failed in eastern Canada, is an example of the potential magnitude of this problem. It is important to note that this problem of icing, while specifically discussed in relation to power lines in this disclosure, is not limited to power lines, but is relevant to all suspended lines where icing can occur (e.g., support lines for towers and lines on a suspension bridge).
Ice Build-up Mechanism
Three types of ice deposits occur under different atmospheric conditions:    (1) Soft rime occurs at temperatures from −3 to −13° C. and a wind velocity from above 0 to 7 m/sec.    (2) Hard rime forms at temperatures from −2 to −9° C. and a wind velocity between 3 to 15 m/sec.    (3) Glaze occurs at temperatures above −4° C. and a wind velocity between 2 to 20 m/sec.
Soft rime is a white, opaque granular deposit of ice. It adheres poorly to conductors and occurs most often in mountainous regions. It is usually formed in supercooled fog. On the windward side, soft rime may grow to long feathery cones, or needles pointing into the wind.
Hard rime is an opaque, granular mass of ice formed by a dense supercooled fog. It is more compact and amorphous than soft rime. It adheres strongly to conductors.
Glaze (blue ice) is a coating of ice, generally clear and smooth, formed by freezing of a film of supercooled water deposited by rain, drizzle, or fog. Glaze is denser, harder, and more transparent than soft or hard rime. It adheres strongly to conductors.
Hard rime and glaze are chiefly responsible for conductor or tower failure as well as conductor galloping.
The Problem and Current Solutions
Ice buildup on high voltage power lines is recognized as a major concern by the utilities, therefore many methods to combat this problem have been devised.
A number of such devices use electrical current and impulses to clear ice from lines. The U.S. Pat. No. 4,690,353 (Haslaim) and the U.S. Pat. No. 5,411,121 (Lafort et al.) describe devices or systems using high intensity electromagnetic impulses to break the ice. In the case of Haslaim, the system is applicable to planar surfaces, and has been developed to remove the ice on the wing of an airplane. Electromagnetic pulses are injected in a thin double ribbon of copper positioned (embedded) in a rubber film. In the case of Laforte et al., the device is applicable to stranded conductors, like a stranded cable. To break the ice, electromagnetic impulses are injected in some of the insulated, integrated conductive wires in the last stranded layer of the cable. These conductive wires are insulated for this purpose during the manufacturing process of the cable. U.S. Pat. No. 6,207,939, entitled “Device And Method For De-Icing An Elongated Structural Element” (to Hydro-Qubec) describes a device that uses pairs of electrically conductive and insulated wires, through which a current is passed causing a repulsion force whose intensity is capable of breaking the ice or the frost on the line.
It appears that the majority of techniques for combating ice buildup on power lines, and many of those being developed or proposed by various research groups and utilities, are based on removing the ice from the line during or after the storm when ice has already formed on the line. Current methods are classified in four domains as (a) General applications convenient to all power lines, (b) Energized conductor applications from 2 km to 100 km, (c) Energized conductor applications shorter than 2 km, and (d) ground wire applications. Also, five type of applications have been identified as passive treatment of conductors/cables (general), active treatment of conductors/cables, internal power on bare conductors, external heat on bare conductors/cables, and external forces on bare conductors/cables.
An analysis of available and proposed approaches shows three different current solutions for combating line icing problems:    1) Reactive Category: This category applies to techniques to shed ice from the line after it has formed. Methods include use of chemical washing (using fluids which promote melting of the ice and its separation from the line), heating (by radiation or by internal or external heating sources including electrical current through the line itself or via heat tracing cable), mechanical forces (using methods to shake the line, such as explosives and hammers, methods involving devices which ride on the line and mechanically remove the ice, methods involving using a high pressure fluid spray wash, etc.), electromagnetic forces (by applying high currents to cause large attractive or repulsive magnetic field between conductors), etc. This category is, currently, the most common approach by the utilities to address ice buildup.
The available or proposed reactive methods generally require access to the line during or after a storm, require expensive equipment, are usually very labor intensive, and/or can be unsafe. Therefore, in addition to being a very expensive solution, they may be not-timely meaning that the power line could fail prior to using such methods.    2) Preventive Category: This category applies to techniques to prevent ice buildup by active or passive methods. The primary method in this category involves coatings. The coating approaches generally involve applying a chemical and/or mechanical coating on the conductor/cable to significantly reduce the bond strength between the ice and the conductor to prevent ice from building up on the line, to develop an interface between the line and the ice that can be activated to cause deicing upon current application, or to absorb radiation energy to melt the ice. There are also some proposed mechanical devices under this category, the most notable is a shape memory alloy “actuator” that provides an axial pull/push device over the line to cause deicing of a section.
The available or proposed coating preventive methods can be costly (coatings need to be reapplied), may have adverse affect on the line, or may be environmentally unsafe. The mechanical methods require extensive energy to activate and unless they have an external source (Reactive category), they only function one time during each temperature transformation (may occur only once during ice storm).    3) Risk Management Category: This category accepts the potential/risk for power line or tower failures and the subsequent power outages and addresses the impact of icing and its consequences. These are mainly economic based approaches involving risk management. However, they can help with identifying and addressing critical areas of the power grid/network where other techniques can be more beneficial.
There is clearly a need for an efficient, simple, self-contained, line-mounted, automatic device for reducing and preventing ice deposits on a suspended line.